New Jersey Governor's Office/Tim Larsen(TRENTON, N.J.) -- Legislative subpoenas could be served to the aides of New Jersey Gov. Chris Christie as early as Monday, sources told ABC News on Sunday.

Christie has been under intense political scrutiny after it was revealed that some of his top political aides shut down key traffic lanes on the George Washington Bridge -- the busiest bridge in the world -- in September for what appear to be politically motivated reasons.

The bridge is one of the most trafficked in the country and leads from New York City directly to the town of Fort Lee, N.J. The lanes were allegedly closed by Christie aides and staffers at the Port Authority of New York and New Jersey, the agency that oversees the bridge, in retribution for the mayor of Fort Lee's refusal to endorse Christie for governor.

Christie has denied any knowledge of the motivation behind the lane closures and so far no evidence has been shown that he knew about the reason for the lane closures.

Originally the closures were said to be part of a traffic study.

Complicating matters for investigators is the fact that the legislative session is scheduled to end on Tuesday, which could mean a legislative subpoena issued on Monday would expire the next day. A special legislative session has been scheduled on Thursday to vote on extending the investigative probe.

Some Democratic lawmakers are saying that Christie could face impeachment hearings if it turns out he knew about the lane closures and authorized them.

Other Republicans have come to Christie's defense. In an appearance today on ABC's This Week, former New York City Mayor Rudy Giuliani said he found it "pretty darn credible" that Christie could have not known about the traffic closure or the motivations behind it.

"Things happen when you're running for re-election," Giuliani said. "The reality is you miss a lot of things."

The headaches certainly aren't over for Christie yet. After facing intense scrutiny, Christie withdrew his nomination for acting attorney general in light of the scandal. State Democrats had delayed the court hearing indefinitely.

ABC News obtained a letter from Fort Lee EMS coordinator Paul Favia that documents four medical situations in which emergency responders were delayed because of the traffic gridlock. In one case, a 91-year-old woman later died at a hospital of cardiac arrest.

Although Favia doesn't directly tie her death to the delays, he noted that "paramedics were delayed due to heavy traffic on Fort Lee Road and had to meet the ambulance en route to the hospital instead of on the scene."